PRELIMINARY  NOTES  ON 

ZLiB^oLoaY  OF  ::i: 

HKJvIISPHAEHICA 

BY 
WILLIAM  L.    VVOODBURN 


Southern  Branch 
of  the 

University  of  California 

Los  Angeles 


Form  L  I 


50? 


PRELIMINARY  NOTES  ON 

THE  EMBRYOLOGY  OF  REBOULIA 

HEMISPHAERICA 


WILLIAM  L.  WOODBURN 


NEW  YORK 
1919 


Reprinted,  without  change  of  paging,  from  the  BULLETIN  OF  THE  TOBREY  BOTANICAL  Ci.ui 
46:  461-464.  pi.  19.    January  21,  1920. 


^ 


SOUTHERN  BRANCr,, 

UNIVERSITY  OF  CALIFORNIA 

LIBRARY, 

ANGELES,  GAL  IF. 


Preliminary  notes  on  the  embryology  of  Reboulia  hemisphaerica 

WILLIAM  L.  WOODBURN 
(WITH  PLATE  19) 

The  object  of  this  paper  is  to  present  a  part  of  a  more  extended 
study  on  the  embryology  and  cytology  of  Reboulia  hemisphaerica 
(L.)  Raddi.  Only  certain  stages  in  the  process  of  fertilization  and 
in  the  early  development  of  the  embryo  sporophyte  will  be  con- 
sidered at  this  time.  The  description  of  various  other  stages  in 
the  life  history  together  with  a  summary  of  the  previous  literature 
on  Reboulia  will  be  left  for  a  subsequent  report. 

FERTILIZATION 

The  male  gamete  in  the  bryophytes  may  undergo  two  series 
of  marked  morphological  changes.  The  first  series  includes  the 
steps  leading  from  the  non-motile  condition  of  the  androcyte 
(the  cell  which  directly  becomes  transformed  into  the  mature 
sperm)  through  the  formation  of  the  actively  motile  free-swim- 
ming sperm.  The  second  series  includes  the  reverse  steps  and 
occurs  in  those  cases  where  a  sperm  reaches  an  egg.  In  this 
second  case  the  motile  sperm  becomes  again  non-motile  with  a 
resting  nucleus  similar  to  that  of  the  androcyte  or  androcyte 
mother-cell.  Details  of  the  main  stages  in  the  first  series  have 
been  carefully  described  for  numerous  liverworts  and  mosses. 
The  processes  accomplished  in  the  second  series,  after  the  sperm 
reaches  the  egg,  are  not  so  well  known.  However,  soon  after 

461 


65587 


462    WOODBURN:  EMBRYOLOGY  OF  REBOULIA  HEMISPHERICA 

reaching  the  egg  the  sperm  nucleus  is  found  to  have  the  form  and 
structure  of  a  nucleus  in  the  resting  stage  (FiG.  i).  Quite  similar 
conditions  have  been  reported  by  Black  (i)  and  Garber  (3)  for 
Riccia  and  by  K.  Meyer  (4)  for  Corsinia.  The  form  and  structure 
of  the  egg  and  sperm  nuclei  at  this  stage  are  to  a  certain  extent 
similar  (FiG.  i).  The  egg  nucleus  is  larger  and  shows  a  coarser 
and  more  open  disposition  of  the  chromatin.  An  unstained  area 
surrounds  the  nucleolus.  A  smaller  nucleolus  is  present  in  the 
sperm  nucleus.  The  latter  as  a  whole  stains  somewhat  more 
heavily  than  does  the  nucleus  of  the  egg. 

The  accompanying  figures  are  drawn  as  nearly  as  possible  in 
that  position  which  is  occupied  in  nature.  For  instance,  the 
necks  of  the  archegonia  at  this  stage  of  development  project  obli- 
quely downward  or  toward  the  substratum.  Consequently  it 
will  be  seen  that,  in  FIG.  I,  the  sperm  nucleus  lies  in  contact  with 
that  side  of  the  egg  nucleus  which  is  toward  the  neck  of  the 
archegonium.  The  membrane  of  the  egg  nucleus  is  somewhat 
infolded  along  the  surface  of  contact. 

Compared  with  corresponding  stages  in  the  life  history  of 
gymnosperms  and  angiosperms  we  know  very  little  concerning 
the  details  of  nuclear  behavior  in  this  and  further  stages  of  fer- 
tilization. 

EARLY  DIVISIONS  OF  THE  EMBRYO 

The  first  division  wall  of  the  zygote  is  laid  down  transversely. 
FIG.  2  represents  the  telophase  of  this  first  division,  with  the  cell 
plate  in  the  process  of  formation.  The  spindle  lies  parallel  with 
the  longitudinal  axis  of  the  venter  of  the  archegonium;  conse- 
quently a  transverse  basal  wall  results  (Fics.  2  and  3).  In 
FIG.  3  the  nuclei  are  in  the  prophase  of  subsequent  division-; 
"a"  represents  the  hypobasal  cell  or  that  one  next  to  the  base  of 
the  archegonium,  and  b,  the  epibasal  cell  or  that  one  next  to 
the  neck  of  the  archegonium.  The  second  division  is  transverse 
and  occurs  in  the  epibasal  cell  (compare  FIGS.  3,  4,  5  and  6). 
The  epibasal  cell  (FiG.  3,  "b"),  with  the  chromosomes  clearly  dif- 
ferentiated, is  in  a  more  advanced  stage  of  prophase  than  the  hypo- 
basal  cell.  There  is  also  evidence  of  centrosomes  or  centrosome- 
like  structures  connected  with  the  nucleus.  FIG.  4  represents 
the  second  division  completed.  Later  stages  (compare  FIGS. 


WOODBURN:   EMBRYOLOGY  OF  REBOULIA  HEMISPHERICA    463 

3,  4,  5,  6  and  n)  indicate  that  from  the  hypobasal  cell  is  devel- 
oped the  foot  and  from  the  epibasal  cell  the  stalk  and  sporangium 
of  the  mature  sporophyte. 

A  third  division  follows  in  either  the  middle  or  apical  cell  of 
the  tier  of  three  (FiG.  4)  which  results  from  the  first  and  second 
divisions.  Compare  FIG.  5,  which  shows  a  tier  or  series  of  four 
cells,  with  FIG.  4.  Then  follows  (FiG.  6)  a  division  in  the  basal  or 
foot  cell  at  right  angles  to  the  first  three  division  walls.  The 
foot  at  this  stage  has  become  quite  dense  in  protoplasmic  contents. 

The  order  of  divisions  just  described  seems  to  represent  the 
usual  conditions.  Compare,  however,  FIGS.  2-6  with  FIGS.  7-10. 
In  each  section  represented  by  FIGS.  7  and  9  there  is  a  triangular- 
shaped  apical  cell,  while  in  FIGS.  8  and  10  both  apical  and  basal 
cells  of  triangular  shape  are  present.  FIG.  1 1  represents  a  slightly 
different  condition,  in  which  the  foot  has  become  divided  into  an 
irregular  group  of  cells. 

In  no  case  do  we  find  the  same  sequence  of  early  divisions  as 
described  by  Cavers  (2).  In  speaking  of  the  early  divisions  of  the 
sporophyte  of  Reboulia,  he  says,  "The  transverse  basal  wall  is 
followed  by  two  sets  of  nearly  equal  vertical  walls  which  intersect 
each  other  at  right  angles,  so  that  the  embryo  shows  a  regular 
octant  stage." 

SUMMARY. 

The  egg  and  sperm  nuclei  are  both  in  a  resting  condition  in  the 
earliest  stages  of  fusion. 

Among  the  Bryophytes  little  is  known  concerning  the  details 
of  nuclear  behavior  during  the  stages  of  fertilization. 

The  earliest  divisions  of  the  zygote  are  transverse.  A  longi- 
tudinal series  or  tier  of  four  cells  may  be  formed. 

Occasionally,  however,  both  apical  and  foot  cells  of  triangular 
outline  may  be  formed,  or  the  basal  cell  may  divide  into  an  irregular 
group  which  constitutes  the  foo.t. 

Of  the  first  two  cells  formed,  the  hypobasal  cell  evidently 
produces  the  foot,  and  the  epibasal  cell  the  stalk  and  sporangium 
of  the  mature  sporophyte. 

NORTHWESTERN  UNIVERSITY, 
EVANSTON,  ILLINOIS 


464    WOODBURN:  EMBRYOLOGY  OF  REBOULIA  HEMISPHERICA 

LITERATURE  CITED 

1.  Black,  Caroline  A.     The  morphology  of   Riccia  Frostii  Aust.     Ann. 

Bot.  27:  511-532.  pi.  37,  38.     1913- 

2.  Cavers,  F.      Contributions  to  the  biology  oi  the  Hepaticae.     Part 
I. —  Targionia,  Reboulia,   Preissia,  Monoclea.     Leeds  and  London. 
March,  1904. 

3.  Garber,  J.  F.     The  life  history  of  Ricciocarpus  natans.     Bot.  Gaz. 
37:  161-177.  pi.  o,  10  +/.  1-4.     1904. 

4.  Meyer,  K.     Untersuchungen  iiber  den  Sporophyt  der  Lebermoose. 

Entwickelungsgeschichte  des  Sporogon  der  Corsinia  marchantioides. 
Bull.  Soc.  Imp.  Nat.  Moscou  1911:  263-286.  pi.  n  +/.  1-22. 
1912. 

Explanation  of  plate  19 

The  figures  were  drawn  by  Miss  Mary  C.  Blair. 

FIG.  i.     Early  stage  of  fusion  of  the  egg  and  sperm  nuclei,  X  1775- 

FIG.  2.     Telophase  of  first  division  of  zygote,  X  565. 

FIG.  3.  First  division  of  zygote  completed;  hypobasal  cell  "a,"  and  epibasal 
cell  "b"  in  prophase  of  subsequent  division,  X  735. 

FIG.  4.     Division  of  epibasal  cell  completed,  showing  tier  of  three  cells,   X  565. 

FIG.  5.     Young  embryo  consisting  of  tier  of  four  cells,  X  565. 

FIG.  6.  Hypobasal  cell  divided  longitudinally;  cell  next  above  in  process  of 
longitudinal  division,  X  565. 

FIG.  7.     Young  embryo  with  wedge-shaped  apical  cell,  X  735. 

FIG.  8.  Young  embryo  with  both  basal  and  apical  cells  triangular  in  shape, 
X735- 

FIG.  9.  Embryo,  older  than  in  any  of  the  preceding  figures,  with  wedge-shaped 
apical  cell  X  565. 

FIG.  10.  Slightly  more  advanced  embryo  than  in  FIG.  9,  showing  both  apical 
and  basal  cells  triangular  in  outline,  X  565. 

FIG.  ii.  Embryo  showing  early  differentiation  of  foot  "a,"  seta  "b,"  and 
capsule  "c,"  X  565. 


65587 


BULL.  TORREY  CLUB 


VOLUME  46,  PLATE  19 


WOODBURN:  EMBRYOLOGY  OF  REBOULIA 


SOUTHERN  BRANCH, 

UNIVERSITY  OF  CALIFORNIA. 


Lithomount 
Pamphlet 

Binder 
Gaylord  Bros. 

Makers 
yracuse,  N.  Y 

PAT.  JAN  21,  1908 


